1. Field of the Invention
The present invention relates generally to surgical instruments. In particular, the present invention relates to improved phacoemulsification needles used in ophthalmic surgery.
2. Description of the Related Art
Phacoemulsification needles are used for breaking apart and removing unwanted tissue and material, particularly cataracts. It should be understood that phacoemulsification procedures can also be used to remove the soft lens of an eye before the soft lens becomes a cataract, and that the procedures described herein for removing cataracts also encompasses such soft lens removal and other common procedures utilizing phacoemulsification. A phacoemulsification needle is typically attached to a handpiece that vibrates the needle at an ultrasonic frequency during a surgical procedure. The phacoemulsification procedure involves using the vibrating needle to ultrasonically fragment a cataract while simultaneously introducing fluid into the eye and withdrawing the fluid and the fragmented cataract particles through the hollow needle. The cataract is emulsified by the distal end tip of the needle and removed from the eye through the hollow needle. A suction source attached to the handpiece is used to supply the necessary suction to the needle.
Current phacoemulsification needles remove nuclear material by use of ultrasound energy, the effect of which forms a combination of cutting and cavitation to fragment the lens. A sharp edge is used to enhance the cutting effect, and this effect is further enhanced by aspiration and vacuum. The needle at the end of the handpiece is hollow, and the edge is typically defined by having a surface with edges that conform to an acute angle (less than 90 degrees) and come to a point. Slicing a hollow metal pipe at any angle will create the sharp edge described.
Fundamentally, the sharp edge of the phacoemulsification probe enhances the cutting ability of the needle, but it poses several dangers. The greatest danger is the ability of the cutting edge to tear intraocular structures while trying to remove the nuclear material. This may result in damage to the lens capsule and iris. Incidentally, the tip passing through the incision itself can cause damage to the incision.
Typically, the sharpened or honed edge is found on both the outer edge of the distal tip of the end of the needle and along the inner edge of the needle (i.e., the outer edge of the lumen). During phacoemulsification, aspiration of eye tissue is achieved by drawing fluid through the inner lumen of the hollow emulsification needle after it has been subjected to ultrasound energy. Even when vacuum is turned off, an imbalance of the flow of fluid to stabilize the anterior chamber of the eye (infusion) and/or the process of the application of ultrasonic energy can create a vacuum-like effect to draw eye structures into the lumen of the phacoemulsification needle with or without intent.
Phacoemulsification needles with sharp edges on any surface can cause damage to ocular tissue. Incidental contact of these sharp edges, either with the sharpened knife-like honing of the edge, or with burrs on the edge remaining from poor manufacturing techniques, will cause damage to the tissues these edges contact. Rounding the outer edge does prevent damage due to an incidental contact. This is analogous to sanding a piece of rough wood to prevent it from snagging on a fabric. Smoothing this outer surface thus prevents damage by either dulling the honed, sharpened surface, or by removing incidental burrs.
The iris is a readily distensible tissue that typically is not involved in intraocular surgery as the dilation is in most cases adequate to keep it out of the field of the active aspiration/emulsification occurring at the distal tip of the phacoemulsification needle. However, as more lens material is removed, the capsule becomes exposed to a greater degree. Likewise, it becomes much more distensible as it becomes more exposed. The anterior capsule is always exposed during phacoemulsification, to a greater degree than the distensible iris. The anterior capsule is perhaps the least distensible of the tissues described, but can be damaged as well.
Damage to the anterior and/or posterior capsule occurs in 2 to 5% of phacoemulsification surgeries, and can be identified as occurring during the use of the phacoemulsification needle in the majority of cases. Damage to the capsule during this stage of surgery significantly compromises the likelihood of successfully removing the cataract without loss of vitreous, and can be shown to compromise the result of the cataract surgery by significantly increasing the intraoperative and postoperative complication rates. The frequency of damage to the iris during cataract surgery is not documented, but can also result in significant compromise of the surgical result.
Techniques to keep distensible eye tissues away from the phacoemulsification needle rely on surgeon ability and instrumentation. Anterior chamber stability is achieved by balancing the inflow of infusion fluid with the removal of this fluid through aspiration. While the phacoemulsification device may be able to achieve this to a large degree, the surgeon-specific technique is the creation of appropriately sized incisions to prevent excess leakage. Such excess leakage can increase outflow and threaten chamber stability. Modifications to phacoemulsification needles have been created to avoid a sudden increase in fluid outflow, called “surge,” which occurs when an absolute or partial occlusion of the phacoemulsification outflow system is suddenly released and outflow exceeds inflow. In addition, surgeon technique may not be sufficient to anticipate unwanted contact of these distensible tissues to the phacoemulsification tip. Situations such as poor iris dilation, an unstable anterior chamber, or surgeon technique can result in an increased likelihood of a distensible eye tissue coming in contact with any of the sharpened or burred edges of a phacoemulsification needle, and this contact is likely to create damage to those eye tissues.
Another problem with prior art phacoemulsification needles is that active aspiration of a distensible ocular tissue can cut or damage that tissue by rubbing it against the sharp internal edge of the distal tip (i.e., the far distal inner edge of the lumen) or against small burrs that may exist despite honing this inner edge surface. As previously discussed, these distensible tissues can be aspirated due to poor chamber stability (such as is seen when the incision sizes are not appropriate and allow excessive outflow), poor iris dilation, or poor surgeon technique as examples. Contact of these tissues with the inner edge of the tip of the phacoemulsification needle (i.e., the outer edge of the inner lumen of the needle) can result in severe damage to these tissues, either from direct cutting of the sharp surface or through ripping or sawing as caused by the roughened burrs.
One possible myth that has arisen from observing the breaking of the capsule after aspirating it into a phacoemulsification tip, or any other hollow intraocular instrument designed for aspiration, is that a “vacuum” break can occur. It is much more likely that the “vacuum” involved merely stabilizes the distensible capsule and allows it to be cut by either the sharpened, honed inner edge, or an incidental burr as a result of poor manufacturing.
A “knuckle” tip for a phacoemulsification needle was demonstrated by Dr. Akahoshi at the ASCRS meeting in April 2004 in San Diego, Calif. This tip resembled the fat end of a pear attached to the end of a phacoemulsification needle, with a central rounded aspirating port. However, the rim of the needle exceeded the standard rim thickness and diameter and was designed to avoid aspirating the capsule. This knuckle-tipped needle requires a new surgical technique to be used by cataract surgeons and a separate device to cut a cataract before removal, thereby reducing surgical efficiency.
Another phacoemulsification needle has been developed by Alcon of Fort Worth, Tex., which has an accessory aspiration port far away from the primary aspirating port at the distal end of the phacoemulsification needle. This port is called the “ABS” port, and is used to stabilize the anterior chamber during phacoemulsification when the primary aspirating tip is occluded. This tip has no role in the direct phacoemulsification of nuclear material, never comes in direct contact with intraocular structures, and is not rounded, dull, detuned or blunt.
There is a need in the industry for an improved phacoemulsification needle that minimizes the risk of damage to a patient's eye, while maintaining its effectiveness and efficiency for phacoemulsification procedures.